Lyocell fiber and manufacturing method therefor

ABSTRACT

The present invention relates to a lyocell fiber, and more specifically to a lyocell fiber, wherein the cross-sectional shape of a monofilament contained in the lyocell fiber is controlled to thus increase the specific surface area of the fiber, thereby exhibiting properties equal or superior to those of conventional lyocell fibers, even when used in a small amount.

TECHNICAL FIELD

The present invention relates to a lyocell fiber, and more particularly to a lyocell fiber having a multi-lobal cross-section.

BACKGROUND ART

Fibers are a natural or artificial filiform object that is flexible and thin and has a large length-to-thickness ratio in terms of the shape thereof. These fibers may be classified into, depending on the morphology thereof, long fibers, mid-length fibers, and short fibers, and may be classified into natural fibers and artificial fibers depending on the type of raw material thereof.

Fibers have long been closely related to human life, and natural fibers such as cotton, hemp, wool, and silk fibers have been used as the main raw materials of clothes. With the advancement of scientific technology since the industrial revolution, the use of fibers has expanded from clothing materials to industrial fields. In order to meet the demand for fiber, which has increased drastically with the development of culture and the increase in the population, pioneering in the field of artificial fibers as new fiber materials is actively being conducted.

Among such artificial fibers, regenerated fibers are not only excellent in tactile and wearing sensations, but are also very fast in moisture absorption and discharge compared to cotton, and thus they have been widely utilized as raw materials for clothes. Particularly, among these regenerated fibers, rayon fibers have excellent gloss and color development properties and may realize a tactile sensation equivalent to that of natural fibers, and furthermore, are also known to be harmless to the human body, and thus are widely employed. However, rayon fibers have easy shrinking and wrinkling properties, and are disadvantageous because the manufacturing process thereof is complicated and environmental problems due to the use of many chemicals during the dissolution of wood pulp, etc. and environmental pollution in the course of wastewater disposal may be caused.

Accordingly, research has been carried out on fibers that are harmless to the environment and human body and exhibit superior properties compared to other existing fibers, and thus lyocell fibers produced from natural pulp and amine oxide hydrate (NMMO) have been introduced these days. Such lyocell fibers have superior tensile properties and fiber properties, such as tactile sensation and the like, compared to conventional regenerated fibers, and do not generate any pollutants during the production process. Because the amine oxide-based solvent may be recycled and may biodegrade upon disposal thereof, lyocell fibers are utilized as environmentally friendly fibers in a variety of fields.

However, since the cross-sectional shape of a lyocell fiber, which is typically produced using amine oxide hydrate as a solvent, is limited to a circular shape, many limitations are imposed on maximizing the advantages of natural fibers and the advantages of synthetic fibers. Therefore, lyocell fibers having a multi-lobal cross-section have been studied with the goal of realizing various properties depending on the cross-sectional shape of the lyocell fiber. However, when lyocell fibers are manufactured through an NMMO dry-wet solution spinning process using an amine oxide hydrate solvent, the spinning solution is discharged via a spinning nozzle, after which the cross-sectional shape of the fiber becomes close to a stable circle during non-coagulation stretching in air present in an air gap, remarkably deteriorating space occupancy for a given nozzle shape.

DISCLOSURE Technical Problem

Accordingly, the present invention is intended to provide a lyocell fiber having a large specific surface area by maximizing a change in the multi-lobal cross-sectional shape and a method of manufacturing the same.

Technical Solution

The present invention provides a lyocell fiber having a multi-lobal cross-section, comprising a lyocell multifilament manufactured by spinning a lyocell spinning dope including a cellulose pulp and an ionic solvent, the multifilament comprising a monofilament having a multi-lobal cross-section, the multi-lobal cross-section of the monofilament including a plurality of projections, and the plurality of projections coming into contact with a first virtual circle and a second virtual circle included in the first virtual circle, being integrally formed with the second virtual circle serving as a center, and coming into contact with the first virtual circle at ends thereof.

Preferably, the multi-lobal cross-section of the monofilament has a multi-lobal ratio of 1.5 to 10, as defined in Equation 1 below.

Multi-lobal ratio=r1/r2  <Equation 1>

In Equation 1, r1 is the radius of the first virtual circle and r2 is the radius of the second virtual circle.

More preferably, the lyocell fiber has a fineness of 1 to 30 denier, the radius of the first virtual circle is 4 to 40 μm, and the radius of the second virtual circle is 2 to 14 μm.

Furthermore, the lyocell fiber may have space occupancy of 200 to 600%, as defined by Equation 2 below.

Space occupancy=(S1/S2)×100(%)  <Equation 2>

In Equation 2, S1 is the area of the first virtual circle, and S2 is the cross-sectional area of the monofilament contained in the lyocell fiber.

Also, the present invention provides a method of manufacturing a lyocell fiber having a multi-lobal cross-section, comprising the steps of: (S1) preparing a lyocell spinning dope including a cellulose pulp and an ionic solvent; (S2) spinning the spinning dope into a multifilament in a coagulation solution including the ionic solvent through a spinning nozzle and simultaneously coagulating the spun multifilament in the coagulation solution; and (S3) water-washing the spun and coagulated multifilament,

The lyocell multifilament thus manufactured comprises a monofilament having a multi-lobal cross-section, the multi-lobal cross-section of the monofilament includes a plurality of projections, and the plurality of projections comes into contact with a first virtual circle and a second virtual circle included in the first virtual circle, is integrally formed with the second virtual circle serving as a center, and comes into contact with the first virtual circle at ends thereof, thus increasing the multi-lobal ratio thereof.

Preferably, the cellulose pulp in the step (S1) contains 85 to 98 wt % of alpha-cellulose.

Furthermore, the ionic solvent is preferably an aqueous solution including at least one ionic compound selected from the group consisting of dibutyl imidazolium acetate, dipentyl imidazolium acetate, dihexyl imidazolium acetate, dipropyl imidazolium octanoate, dibutyl imidazolium octanoate, 1-ethyl-3-methyl imidazolium heptanoate, 1-ethyl-3-methyl imidazolium octanoate, 1-ethyl-3-methyl imidazolium nonanoate, 1-ethyl-3-methyl imidazolium decanoate, 1-ethyl-3-methyl imidazolium undecanoate, 1-ethyl-3-methyl imidazolium dodecanoate, 1-ethyl-3-methyl imidazolium diethyl phosphate, diethyl imidazolium octanoate, 1-decyl-3-methyl imidazolium acetate, and 1-ethyl-3-methyl imidazolium acetate. More preferably, the ionic solvent in the step (S1) is an aqueous solution in which the concentration of the ionic compound is 95% or more.

Preferably, the lyocell spinning dope in the step (S1) includes 6 to 25 wt % of the cellulose pulp and 75 to 94 wt % of the ionic solvent, and the ionic solvent contained in the coagulation solution in the step (S2) is an aqueous solution in which the concentration of the ionic compound is 20 to 70% and the temperature of the coagulation solution is 30 to 80° C.

Advantageous Effects

According to the present invention, a lyocell fiber imparted with a large specific surface area by maximizing a change in a multi-lobal cross-sectional shape and a method of manufacturing the same can be provided, and the lyocell fiber having a multi-lobal cross-section according to the present invention is used as a reinforcement in the fields of clothing, construction or vehicles, thereby exhibiting properties equal or superior to those of conventional lyocell fibers, even when used in a small amount.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 schematically shows the multi-lobal cross-sectional shape of a monofilament contained in a lyocell fiber having a multi-lobal cross-section according to an embodiment of the present invention; and

FIG. 2 shows the cross-section of a lyocell fiber manufactured in Example 1 according to the present invention.

DESCRIPTION OF REFERENCE NUMERALS IN THE DRAWINGS

1: center, 2: projection, 3: long axis of projection, 4: recess of projection, 5: end of projection

11: first virtual circle, 12: second virtual circle

BEST MODE

Hereinafter, a detailed description will be given of the present invention.

The present invention addresses a lyocell fiber having a multi-lobal cross-section, comprising a lyocell multifilament manufactured by spinning a lyocell spinning dope including a cellulose pulp and an ionic solvent, in which the multifilament is composed of a monofilament having a multi-lobal cross-section, the multi-lobal cross-section of the monofilament includes a plurality of projections, and the plurality of projections comes into contact with a first virtual circle and a second virtual circle included in the first virtual circle, and comes into contact with the first virtual circle at ends thereof.

[Multi-Lobal Cross-Section]

As used herein, the term “multi-lobal cross-section” refers to a cross-sectional shape of a monofilament including a plurality of projections. Specifically, as shown in FIG. 1, it indicates a cross-section configured to include a plurality of projections 2, which are integrally formed with a center 1.

More specifically, the size and shape of the multi-lobal cross-section may be defined within the range of a first virtual circle 11, formed by connecting the end points of the projections 2, and a second virtual circle 12 included in the first virtual circle 11. Here, the first virtual circle 11 is a circle having a radius greater than that of the second virtual circle 12, and these circles may or may not be concentric.

The multi-lobal cross-section, having a plurality of projections 2, is configured such that a plurality of projections 2 are integrally formed with the center 1 overlapping the second virtual circle 12, in which the end 5 of each of the projections is in contact with the first virtual circle 11 to thus form the long axis 3 of the projection 2, and in which the recesses 4 formed between the projections are in contact with the second virtual circle 12.

In the present invention, in order to maximize the specific surface area of the lyocell fiber, the multi-lobal cross-section may include three projections.

The multi-lobal cross-section of the monofilament preferably has a multi-lobal ratio of 1.5 to 10, as defined by Equation 1 below.

Multi-lobal ratio=r1/r2  <Equation 1>

Here, r1 is the radius of the first virtual circle and r2 is the radius of the second virtual circle.

If the multi-lobal ratio is less than 1.5, the cross-section becomes close to a circular shape, and thus the difference in specific surface area from the circular cross-section is not significant, making it impossible to achieve the desired properties of a multi-lobal fiber according to the present invention. On the other hand, if the multi-lobal ratio exceeds 10, it is difficult to control the manufacturing process, and the connections between the virtual circles in the monofilament and the ends of the projections become thin, making it difficult to maintain spinning stability. As such, when the multi-lobal ratio of the multi-lobal cross-section approximates 10, a larger specific surface area may be favorably obtained, but even at a multi-lobal ratio of about 5 to 9.7, the increase in the surface area compared to conventional filaments having a circular cross-section may become significant. According to an embodiment of the present invention, the multi-lobal ratio may fall in the range of 5.87 to 9.6.

The fineness of the lyocell fiber according to the present invention is 1 to 30 denier, the radius of the first virtual circle is 4 to 40 μm, and the radius of the second virtual circle is 2 to 14 μm. If the radius of the first virtual circle or the second virtual circle is less than the above lower limit, the fineness of the monofilament is excessively decreased and the discharge rate and pressure may be lowered to a level at which it is impossible to spin a filament, making it impossible to form a filament. On the other hand, if the radius thereof exceeds the about upper limit, solvent extrusion becomes inefficient and thus the contact between filaments occurs, undesirably making it impossible to form a uniform cross-sectional shape of the filament.

The monofilament contained in the lyocell fiber of the present invention may have the multi-lobal cross-section mentioned above, and the lyocell fiber may have space occupancy of 200 to 600%, as defined in Equation 2 below.

Space occupancy (%)=(area of first virtual circle/cross-sectional area of monofilament contained in lyocell fiber)×100  <Equation 2>

Space occupancy is the proportion of space in a fiber substantially occupied by the monofilament due to the projections of the multi-lobal cross-section. In the case where the cross-section of a monofilament contained in a lyocell fiber has a circular shape, the cross-sectional area of the actual monofilament is equal to the area of the first virtual circle, and thus the space occupancy defined as above is 100%. However, in the case of a fiber having a multi-lobal cross-section having projections, the actual area of the fiber becomes large due to the projections. As the space occupancy increases, the specific surface area of the fiber may become large.

In the present invention, the lyocell fiber may have space occupancy of 220% or more, and preferably 250% or more, as defined in Equation 2, in order to increase a specific surface area so that volume properties or other properties such as interfacial adhesion properties, quick-drying properties, etc. become superior. In an embodiment of the present invention, the space occupancy thereof may be realized even to a range of 426.3% to 574.1%.

According to the present invention, a method of manufacturing a lyocell fiber having a multi-lobal cross-section includes the steps of (S1) preparing a lyocell spinning dope including a cellulose pulp and an ionic solvent, (S2) spinning the spinning dope into a multifilament in a coagulation solution including the ionic solvent via a spinning nozzle having a plurality of recesses having a shape complementary to a multi-lobal shape and simultaneously coagulating the spun multifilament in the coagulation solution, and (S3) water-washing the spun and coagulated multifilament.

The lyocell multifilament thus obtained is composed of a monofilament having a multi-lobal cross-section, and the multi-lobal cross-section of the monofilament has a plurality of projections, and the plurality of projections comes into contact with a first virtual circle and a second virtual circle included in the first virtual circle, is integrally formed with the second virtual circle serving as a center, and comes into contact with the first virtual circle at ends thereof, thereby increasing the multi-lobal ratio.

[Step (S1)]

(S1) is a step of preparing a lyocell spinning dope including a cellulose pulp and an ionic solvent.

The lyocell spinning dope may include 6 to 25 wt % of the cellulose pulp and 75 to 94 wt % of the ionic solvent, and the cellulose pulp preferably contains 85 to 98 wt % of alpha-cellulose, and additionally, preferably has a degree of polymerization (DPw) of 600 to 1700.

In the lyocell spinning dope, if the amount of cellulose pulp is less than 6 wt %, the viscosity of the prepared spinning dope is low and thus it is difficult to realize a fibrous shape upon spinning. On the other hand, if the amount thereof exceeds 25 wt %, the solubility of the ionic solvent, having high polarity, may decrease, making it difficult to perform the dissolution process.

In the lyocell spinning dope, if the amount of the ionic solvent is less than 75 wt %, the dissolution viscosity may significantly increase, and thus the extent of discharge from the nozzle may decrease and solvent extraction may become difficult. On the other hand, if the amount thereof exceeds 94 wt %, the spinning viscosity may significantly decrease, making it difficult to prepare a uniform fiber during the spinning process.

Here, the ionic solvent is preferably an aqueous solution including at least one ionic compound selected from the group consisting of dibutyl imidazolium acetate, dipentyl imidazolium acetate, dihexyl imidazolium acetate, dipropyl imidazolium octanoate, dibutyl imidazolium octanoate, 1-ethyl-3-methyl imidazolium heptanoate, 1-ethyl-3-methyl imidazolium octanoate, 1-ethyl-3-methyl imidazolium nonanoate, 1-ethyl-3-methyl imidazolium decanoate, 1-ethyl-3-methyl imidazolium undecanoate, 1-ethyl-3-methyl imidazolium dodecanoate, 1-ethyl-3-methyl imidazolium diethyl phosphate, diethyl imidazolium octanoate, 1-decyl-3-methyl imidazolium acetate, and 1-ethyl-3-methyl imidazolium acetate. Here, the concentration of the ionic compound is preferably 95% or more.

[Step (S2)]

(S2) is a step of discharging the lyocell spinning dope spun in the step (S1) into the coagulation solution of a coagulation bath from the spinning nozzle of a spinneret and coagulating the discharged multifilament in the coagulation solution.

Here, the temperature of the spinning dope may fall in the range of 30 to 90° C.

The spinneret has a plurality of spinning holes, and the shape of the spinning holes may vary depending on the end use and desired morphology, taking into consideration the hole area and the slit size suitable for the shape of the multi-lobal cross-section to be manufactured, and the number of spinning holes may be set within the range of 300 to 50,000 in consideration of the number of monofilaments in the multifilament to be manufactured.

In the present invention, when the spinning dope is discharged through the spinning nozzle, the spinning nozzle is disposed so that the spinning dope is discharged toward the inside of the coagulation solution, whereby the multifilament is coagulated in the coagulation solution as soon as it is discharged through the spinning nozzle. The coagulation is preferably performed in the state in which the shape upon discharge through the nozzle is maintained without change.

Here, in order to realize appropriate coagulation, the ionic solvent contained in the coagulation solution is preferably the same kind as the ionic solvent used in the step (S1), thereby making it easy to recover and recycle the solvent. Preferably useful is an aqueous solution in which the concentration of the ionic compound in the coagulation solution is set to the range of 20 to 70%. When the concentration of the ionic compound of the ionic solvent contained in the coagulation solution is maintained at 20% or more, the rate of coagulation of the fiber discharged from the spinning nozzle is prevented from increasing excessively, and thus crystal-controlled amorphous fiber portions may be ensured, thereby increasing elongation. When the concentration thereof is maintained at 70% or less, the rate of coagulation is prevented from decreasing excessively, thus inducing crystal growth, thereby increasing crystallinity, ultimately enhancing strength.

Furthermore, the temperature of the coagulation solution is maintained in the range of 30 to 80° C., whereby the rate of diffusion of the fiber discharged from the spinning nozzle into the solvent may be set to an appropriate level, whereby the elongation of the fiber discharged from the spinning nozzle is properly maintained, thus easily controlling the physical properties thereof.

[Step (S3)]

(S3) is a step of water-washing the lyocell multifilament obtained in the step (S2). Specifically, the lyocell multifilament obtained in the step (S2) is placed in a traction roller and then in a water-washing bath, and is thus washed with water.

In the step of water-washing the filament, a water-washing solution at 0 to 100° C. may be used, taking into consideration the recovery and reuse of the solvent after the water-washing process. The water-washing solution may include water, and may further include other components as necessary.

The water-washed lyocell filament may be subjected to solvent extraction in the coagulation bath and stretching and shrinking due to processing tension, and the concentration and temperature of the water-washing solution should be kept constant in order to exhibit uniform properties.

The lyocell multifilament water-washed in the step (S3) may be subjected to oiling treatment as necessary, followed by drying and winding. Unless there is a need for oiling treatment, drying and winding may be performed after the water-washing process.

The oiling treatment may be performed by completely soaking the multifilament in oil, and the amount of oil taken up by the filament may be maintained constant based on a pressure difference between the press rollers provided to the entry roll and the release roll of an oiling device. The oil functions to decrease the friction of the filament upon contact with the drying roller and the guide during subsequent processing.

As mentioned above, the lyocell fiber of the present invention is biodegradable and is thus environmentally friendly.

Furthermore, the lyocell fiber of the present invention is configured such that the monofilament has a multi-lobal cross-sectional shape including a plurality of projections, and thus the specific surface area thereof is increased. Even when the lyocell fiber of the invention is used in a small amount compared to conventional fibers, including lyocell fibers having a circular cross-section and lyocell fibers having a low multi-lobal ratio, properties equal or superior to those of the conventional fibers may be exhibited.

In particular, even when the lyocell fiber of the present invention, having a large specific surface area, is used in a small amount as a reinforcement or the like in the fields of clothing, construction or vehicles, equal or superior properties may be exhibited, compared to conventional lyocell fibers.

More specifically, when the lyocell fiber according to the present invention is used for clothing, it exhibits excellent moisture-absorbing and quick-drying properties due to its large specific surface area. Therefore, even when sweat is discharged, there is no clinging to the wearer's body, which keeps the skin comfortable and reduce discomfort. Also, since the cooling rate is high, rapid cooling may be continuously maintained when sweat is continuously discharged. Here, the application range of clothing may include, but is not limited to, outdoor wear, sportswear, t-shirts, golf wear, men's and women's wear, functional innerwear, hats, sports socks, undergarments, wet tissues, mask packs, and the like.

When the lyocell fiber according to the present invention is used as a reinforcement, the larger the contact area with the material to be reinforced, the greater the reinforcing function. Also, it may be applied to mechanical rubber goods (MRGs) such as tire cords or hose reinforcements, cement reinforcements, vehicle interior materials, and tobacco filter materials.

MODE FOR INVENTION

A better understanding of the present invention will be given through the following examples, which are merely set forth to illustrate, but are not to be construed as limiting the scope of the present invention, as will be apparent to those skilled in the art.

Example 1

A 6 wt % spinning dope for manufacturing a lyocell fiber was prepared by dissolving 13.2 g of a cellulose pulp having a DPw of 820 and 93.9 wt % of alpha-cellulose in 206.8 g of a 1-ethyl-3-methyl imidazolium acetate solvent (having a concentration of 97% therein).

Specifically, the spinning dope was spun at a spinning temperature of 50° C. using the spinning nozzle of a spinneret having a plurality of unit holes each having three holes (a spinning nozzle having a slit of 0.06 mm and a length of 0.254 mm), while adjusting the amount of the spinning dope that was discharged and the spinning rate so that the fineness per filament was 3.0 denier. The filaments discharged from the spinning nozzle were fed into a coagulation bath.

The coagulation solution in the coagulation bath had a temperature of 70° C. and was composed of 50 wt % water and 50 wt % 1-ethyl-3-methyl imidazolium.

The formed filaments were passed through a 6-stage water-washing bath using a traction roller to thus remove the remaining 1-ethyl-3-methyl imidazolium acetate, and furthermore, the filaments were uniformly soaked with oil and then pressed so that the filaments had an oil content of 0.2%, and then dried at 150° C. using a drying roller, thus obtaining a lyocell fiber having a fineness of 3.0 denier, including a multifilament comprising a monofilament having a multi-lobal cross-section with three projections. The cross-section of the lyocell fiber of Example 1 is shown in FIG. 2.

Example 2

A lyocell fiber including a multifilament comprising a monofilament having a multi-lobal cross-section with three projections was manufactured in the same manner as in Example 1, with the exception that the amount of the spinning dope that was discharged and the spinning rate were adjusted so that the fineness per filament was 6.9 denier.

Example 3

A lyocell fiber including a multifilament comprising a monofilament having a multi-lobal cross-section with three projections was manufactured in the same manner as in Example 1, with the exception that the amount of the spinning dope that was discharged and the spinning rate were adjusted so that the fineness per filament was 10 denier.

Comparative Example 1

A lyocell fiber including a multifilament comprising a monofilament having a circular cross-section was manufactured in the same manner as in Example 1, with the exception that a spinneret having a plurality of unit holes, each comprising a single circular hole, was used, and the amount of the spinning dope that was discharged and the spinning rate were adjusted so that the fineness per filament was 3.0 denier.

Comparative Example 2

A lyocell fiber including a multifilament comprising a monofilament having a circular cross-section was manufactured in the same manner as in Comparative Example 1, with the exception that the amount of the spinning dope that was discharged and the spinning rate were adjusted so that the fineness per filament was 6.0 denier.

Comparative Example 3

A lyocell dry-wet spinning dope was prepared by mixing a cellulose pulp having a DPw of 820 and 93.9 wt % of alpha-cellulose with an NMMO/H₂O solvent mixture (at a weight ratio of 90/10) containing 0.01 wt % of propyl gallate so that the amount of the cellulose pulp was 12 wt % (which means that the concentration of the spinning dope was 12%) based on the total weight of the mixture.

Next, the spinning dope was spun at a spinning temperature of 110° C. from a spinning nozzle in the same form as the nozzle used in Example, while adjusting the amount of the spinning dope that was discharged and the spinning rate so that the fineness per filament was 3.2 denier. The filamentary spinning dope discharged from the spinning nozzle was continuously fed into a coagulation solution in a coagulation bath through an air gap.

The spinning dope was primarily coagulated using cooling air at 8° C. and a wind velocity of 10 m/s in the air gap. The coagulation solution had a temperature of 25° C. and was composed of 85 wt % water and 15 wt % NMMO. As such, the concentration of the coagulation solution was continuously monitored using a sensor and a refractometer.

Subsequently, the filaments stretched in the air layer while passing through a traction roller were washed with a water-washing solution sprayed using a water-washing device to remove the remaining NMMO, and furthermore, the filaments were uniformly soaked with oil and then pressed so that the filaments had an oil content of 0.2%, and then dried at 150° C. using a drying roller, thus obtaining a lyocell multifilament having a fineness of 3.2 denier, comprising a monofilament having a multi-lobal cross-section with three projections.

Comparative Example 4

A lyocell multifilament having a multi-lobal cross-section with three projections was manufactured in the same manner as in Comparative Example 3, with the exception that the amount of the spinning dope that was discharged and the spinning rate were adjusted so that the fineness per filament was 6.9 denier.

The lyocell fibers manufactured in Examples and Comparative Examples were measured to determine the cross-sectional shape of the monofilament contained therein, fineness and space occupancy through the following methods. The results are shown in Table 1 below.

(1) Cross-sectional shape of monofilament contained in lyocell fiber: a small bundle of fibers was sampled, rolled with a black cotton pad, made thin, inserted into a hole in a plate that was used to transversely cut the fiber, and then cut using a razor blade so that the cross-section was not pushed. The cross-section thereof was observed at a predetermined magnification using an optical microscope (BX51, Olympus), and the image thereof was stored using a digital camera. The cross-sectional image of the fiber was treated in a manner in which the cross-section to be determined could be specified and the radius and area thereof were analyzed using the Olympus soft imaging solution program.

(2) Fineness: The cross-sectional area of the monofilament of the actual lyocell fiber obtained through the cross-sectional analysis and the density of the lyocell fiber were substituted into Equation 3 below to give the fineness of the lyocell fiber.

Fineness (De)=[cross-sectional area of monofilament of lyocell fiber (μm²)×density of lyocell fiber (g/cm³)×9000 (m)]/1000000  <Equation 3>

-   -   Density of lyocell fiber=1.49 g/cm³

TABLE 1 Cross-sectional shape of monofilament contained in lyocell fiber Cross- sectional area of Radius monofilament Radius of Area of of of first second first actual Multi- virtual virtual virtual lyocell lobal Space circle circle circle fiber Fineness ratio occupancy (r1, μm) (r2, μm) (μm²) (μm²) (De) (r1/r2) (%) Ex. 1 20.62 2.15 1336.2 232.73 3.0 9.6 574.1 Ex. 2 24.77 3.82 1928.66 361.74 6.9 6.47 533.1 Ex. 3 32.92 5.69 3458.40 811.23 10.0 5.87 426.3 Comp. 8.46 8.46 225.23 225.23 3.0 1 100 Ex. 1 Comp. 11.97 11.97 450.45 450.45 6.0 1 100 Ex. 2 Comp. 11.30 6.08 401.37 244.59 3.2 1.85 164.1 Ex. 3 Comp. 17.99 6.73 1017.58 514.58 6.9 2.67 197.7 Ex. 4

As is apparent from Table 1, the lyocell fibers of Examples 1 to 3, comprising monofilaments having a multi-lobal cross-section, exhibited great space occupancy compared to Comparative Examples 1 and 2, comprising monofilaments having a circular cross-section, and compared to the multi-lobal lyocell fibers manufactured through the dry-wet spinning process using the same nozzle form in Comparative Examples 3 and 4.

Based on the above results, the lyocell fibers of Examples 1 to 3 can be found to have a large specific surface area, and can thus be widely applied in fields requiring fibers having a large specific area.

Although specific embodiments of the present invention have been disclosed in detail as described above, it is obvious to those skilled in the art that such description is merely of preferable exemplary embodiments and is not construed to limit the scope of the present invention. Therefore, the substantial scope of the present invention will be defined by the appended claims and equivalents thereof. 

1. A lyocell fiber having a multi-lobal cross-section, comprising a lyocell multifilament manufactured by spinning a lyocell spinning dope including a cellulose pulp and an ionic solvent, the multifilament comprising a monofilament having a multi-lobal cross-section, the multi-lobal cross-section of the monofilament including a plurality of projections, and the plurality of projections coming into contact with a first virtual circle and a second virtual circle included in the first virtual circle, being integrally formed with the second virtual circle serving as a center, and coming into contact with the first virtual circle at ends thereof.
 2. The lyocell fiber of claim 1, wherein the multi-lobal cross-section has a multi-lobal ratio of 1.5 to 10, as defined in Equation 1 below: Multi-lobal ratio=r1/r2  <Equation 1> wherein r1 is a radius of the first virtual circle and r2 is a radius of the second virtual circle.
 3. The lyocell fiber of claim 2, wherein the lyocell fiber has a fineness of 1 to 30 denier, the radius of the first virtual circle is 4 to 40 μm, and the radius of the second virtual circle is 2 to 14 μm.
 4. The lyocell fiber of claim 1, wherein the lyocell fiber has a space occupancy of 200 to 600%, as defined by Equation 2 below: Space occupancy=(S1/S2)×100(%)  <Equation 2> wherein S1 is an area of the first virtual circle and S2 is a cross-sectional area of the monofilament contained in the lyocell fiber.
 5. The lyocell fiber of claim 1, wherein the cellulose pulp contains 85 to 98 wt % of alpha-cellulose.
 6. The lyocell fiber of claim 1, wherein the ionic solvent is an aqueous solution including at least one ionic compound selected from the group consisting of dibutyl imidazolium acetate, dipentyl imidazolium acetate, dihexyl imidazolium acetate, dipropyl imidazolium octanoate, dibutyl imidazolium octanoate, 1-ethyl-3-methyl imidazolium heptanoate, 1-ethyl-3-methyl imidazolium octanoate, 1-ethyl-3-methyl imidazolium nonanoate, 1-ethyl-3-methyl imidazolium decanoate, 1-ethyl-3-methyl imidazolium undecanoate, 1-ethyl-3-methyl imidazolium dodecanoate, 1-ethyl-3-methyl imidazolium diethyl phosphate, diethyl imidazolium octanoate, 1-decyl-3-methyl imidazolium acetate, and 1-ethyl-3-methyl imidazolium acetate.
 7. A method of manufacturing a lyocell fiber having a multi-lobal cross-section, comprising the steps of: (S1) preparing a lyocell spinning dope including a cellulose pulp and an ionic solvent; (S2) spinning the spinning dope into a multifilament in a coagulation solution including the ionic solvent through a spinning nozzle and simultaneously coagulating the spun multifilament in the coagulation solution; and (S3) water-washing the spun and coagulated multifilament, wherein a lyocell multifilament manufactured through the steps (S1) to (S3) comprises a monofilament having a multi-lobal cross-section, the multi-lobal cross-section of the monofilament includes a plurality of projections, and the plurality of projections comes into contact with a first virtual circle and a second virtual circle included in the first virtual circle, and comes into contact with the first virtual circle at ends thereof.
 8. The method of claim 7, wherein the cellulose pulp in the step (S1) contains 85 to 98 wt % of alpha-cellulose.
 9. The method of claim 7, wherein the lyocell spinning dope in the step (S1) includes 6 to 25 wt % of the cellulose pulp and 75 to 94 wt % of the ionic solvent.
 10. The method of claim 7, wherein the ionic solvent in the step (S1) is an aqueous solution in which a concentration of the ionic compound is 95% or more.
 11. The method of claim 7, wherein the ionic solvent contained in the coagulation solution in the step (S2) is an aqueous solution in which a concentration of the ionic compound is 20 to 70%, and a temperature of the coagulation solution is 30 to 80° C.
 12. The method of claim 10, wherein the ionic compound is at least one selected from the group consisting of dibutyl imidazolium acetate, dipentyl imidazolium acetate, dihexyl imidazolium acetate, dipropyl imidazolium octanoate, dibutyl imidazolium octanoate, 1-ethyl-3-methyl imidazolium heptanoate, 1-ethyl-3-methyl imidazolium octanoate, 1-ethyl-3-methyl imidazolium nonanoate, 1-ethyl-3-methyl imidazolium decanoate, 1-ethyl-3-methyl imidazolium undecanoate, 1-ethyl-3-methyl imidazolium dodecanoate, 1-ethyl-3-methyl imidazolium diethyl phosphate, diethyl imidazolium octanoate, 1-decyl-3-methyl imidazolium acetate, and 1-ethyl-3-methyl imidazolium acetate.
 13. The method of claim 7, wherein the multi-lobal cross-section of the monofilament has a multi-lobal ratio of 1.5 to 10, as defined in Equation 1 below: Multi-lobal ratio=r1/r2  <Equation 1> wherein r1 is a radius of the first virtual circle and r2 is a radius of the second virtual circle.
 14. The method of claim 11, wherein the ionic compound is at least one selected from the group consisting of dibutyl imidazolium acetate, dipentyl imidazolium acetate, dihexyl imidazolium acetate, dipropyl imidazolium octanoate, dibutyl imidazolium octanoate, 1-ethyl-3-methyl imidazolium heptanoate, 1-ethyl-3-methyl imidazolium octanoate, 1-ethyl-3-methyl imidazolium nonanoate, 1-ethyl-3-methyl imidazolium decanoate, 1-ethyl-3-methyl imidazolium undecanoate, 1-ethyl-3-methyl imidazolium dodecanoate, 1-ethyl-3-methyl imidazolium diethyl phosphate, diethyl imidazolium octanoate, 1-decyl-3-methyl imidazolium acetate, and 1-ethyl-3-methyl imidazolium acetate. 